1. Field of the Invention
The present invention relates to a coil antenna device, and more particularly to a coil antenna device that includes a core including a magnetic layer and a coil conductor arranged in the core such that a portion of the magnetic layer defines a magnetic core and such that a coil axis extends along a principle surface of the core.
2. Description of the Related Art
The present invention also relates to an antenna module in which a plurality of wireless communication devices for use in wireless communication, which includes a coil antenna device, is mounted on a printed wiring board.
An example of such coil antenna devices is disclosed in Japanese Unexamined Patent Application Publication No. 2009-284476. According to this background art, a magnetic antenna is formed such that an electrode material is arranged in a coil shape around a center core composed of a magnetic material and a non-magnetic material. Further, an insulation layer is formed on one or both of exterior side surfaces of the coiled electrode material. Further, a cross-section of the core, which is cut in a direction perpendicular to a magnetic flux, is configured such that the magnetic material is divided by the non-magnetic material. According to the foregoing configuration, reduction in size and improvement in communication sensitivity are achieved together.
Here, the “coil antenna” is a device that wirelessly communicates with an antenna of a communicating party on the other side through a magnetic field produced in a coil conductor. As frequencies of wireless signals, HF bands are mostly used.
However, in the background art, the coiled electrode material is wound on the surface of the core, thereby producing a magnetic field that expands evenly in the core's side surface directions and principle surface directions. This may cause magnetic field formation failures due to interference between a metal object mounted near the magnetic antenna and the magnetic field, and thus lead to deterioration in wireless communication performance. It is particularly worrying that sufficient communication distance may not be secured, or that communication characteristics may vary when the mounting position of the metal object is changed.